Merle was turned into a zombie after his death and was ultimately put down by his brother Daryl (Norman Reedus) in the final moments of the episode.

Roberts – who plays The Governor's scientist Milton Mamet – told E! News that he was as surprised as anyone to learn about Merle's death.

"This is how close they keep their information to the vest," he said. "Milton didn't appear in episode 315, which was yesterday, so Dallas the actor never got the script."

He continued: "So when I showed up to shoot episode 316, I went in the makeup trailer and saw a picture of Merle as a walker. That's how I found out. That's how closely guarded all of those secrets are."